Nothing that is a derived work from the original LPMud can be used for profit. That includes LDMud, MudOS and FluffOS.

Shattered World (http://sourceforge.net/projects/swlpc/) claims to be sufficiently separated from LPMud to not fall into that situation. If you accept their view (and I haven't looked into it deeply enough to have a strong opinion one way or the other) then you can use their driver under the GPL, for commercial use.

DGD can be used for a commercial mud, but not under the default license. You need to obtain a specific license for commercial usage. The process for obtaining that license has changed over the years, I'm not sure what the current process is, but the DGD site probably says.

Terebi (http://www.terebi.us/) has an explicit goal to allow it to be used for a commercial MUD, but it's not yet complete enough to really be a viable option.

Following from Dworkin's recent announcement you can now use DGD 1.4 for a commercial MUD without paying a license fee.

So, if you want to create a from scratch, pay-to-play, LPC based MUD without paying any licensing fees, then DGD 1.4 is your best option.If you're willing to pay a license fee, then DGDMP is probably a better choice (but I've never used it)

Neither of those a particularly good options is you have an existing LPMud or MudOS/FluffOS MUD, as the port to DGD would be a lot of work. If you are in that situation then you don't currently have a lot of options.